Pressurized knotter screen



March 10, 1970 s. M. SALOMON 3,499,528

PRESSURIZED KNOTTER SCREEN Filed May 21. 1968 2 Sheets-Sheet 1 INVENTOR. I

z j 4 ATTORNEYS March 10, 1970 s. M. SALOMON 3,

PRESSURIZED KNOTTER SCREEN Filed May 21, 1968 2 Sheets-Sheet 2 I N VEN'TOR. ficz iomazzfllazzzazz BY 4 i ATTORNEYS United States Patent 3,499,528 PRESSURIZED KNOTTER SCREEN Salomon M. Salomon, Madison, Wis., assignor to Beloit Corporation, Beloit, Wis., a corporation of Wisconsin Filed May 21, 1968, Ser. No. 730,884 Int. Cl. B07d N04 US. Cl. 209-273 3 Claims ABSTRACT OF THE DISCLOSURE A screening apparatus for removing knots and large wood chips from a slurry of Wood pulp. The screening apparatus includes a stock screen which has a plurality of foils each of which comprises tWo members. One of the members of each foil pivots about the other so as to have an active and passive position. Connected to the stock screen is a centrifugal separator, sump settling chamber and a rotary star valve which provide continuous removal of the undesired stock containing knots and large wood chips.

BACKGROUND OF THE INVENTION Field of the invention This invention relates generally to apparatus for screening of particles from liquids such as paper making or the like, Specifically, the preesnt invention is directed to a pressure stock screen which includes a specially shaped foil means for the handling and removal of knots or the like from the stock.

One example of knots is undefibered wood chips that occur in chemical wood pulp due to incomplete disgestion of the imperfect character of the wood chip. Another example is undefibered wood chips in groundwood pulp that have accidentally passed through the defibering mechanism. Yet another example is undefibered clumps of wastepaper held together by metal fasteners that occur in wastepaper pulp. Still another example is the large non-fibrous impurities which may accidentally be present such as glass, brick chips, metal or plastic materials. Therefore, the fibrous materials being of generally large configuration fall in the category of knots and therefore the term knots refers to any large fibrous object which must be removed from the pulp.

Description of the prior art In the process of refining wood to produce wood pulp for paper making, a continuous search for better groundwood has introduced a method known as chip groundwood which is based on high consistency refining of chips. Usually, two or three stages of refining are involved and the stock is often thickened to the proper level before reaching the next stage. This type of refining often produces many large undesirable chips in the end product and therefore the pulp must be subjected to a knotter screen to remove the undesired large chips.

SUMMARY OF THE INVENTION 3,499,528 Patented Mar. 10, 1970 Briefly, the screening device of the present invention is capable of operating under extremely high loads of undefibered pulp, which may result in the general collapse of the screening elements within the device. This situation may arise in high-yield pulping systems, when due to raw cooks, the refiner discs following the blow tank are separated to increase the clearance and decrease the load between the discs. This allows large quantities of undefibered materials to be sent to the screening device.

Therefore, yet another object of the present invention is to provide a screening device for removing knots and large undefibered chips without allowing the knots or chips ot be subjected against the screening element within the device.

A feature of the present invention is the use of a plurality of rotating foils, each foil including a pivotable element which acts in one position as a doctor blade, and in another position to subject the knots and chips to centrifugal force into a centrifugal separator formed as an integral part of the screening device.

BRIEF DESCRIPTION OF THE DRAWINGS These and other objects, features and advantages will be more fully realized and understood from the following details and description when taken in conjunction with the accompanying drawings wherein:

FIGURE 1 is an elevational view which is partially broken away in vertical section to show the screening apparatus constructed in accordance with this invention;

FIGURE 2 is a partial top plan view of a screen and foil associated with the screening apparatus of FIGURE FIGURE 3 is a plan view of the foil of FIGURE 2; and

FIGURE 4 illustrates an external centrifugal separator, a sump settling chamber and a rotary star valve used in accordance with this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIGURE 1 illustrates a screening apparatus constructed in accordance with the principles of this invention and includes a stock screen designated generally by reference numeral 10. The stock screen 10 includes a base 11 supporting a main body 12 of substantially cylindrical configuration. An inlet 14 is provided near the upper portion of the body 12 for receiving a supply of fibrous material suspended in liquid such as paper stock. The material is delivered to a chamber 15 within the housing 12 whereupon the desired constituent of the material passes through a screen member 1 6 and is collected by an outlet receiving chamber 17. The annular screen member 16, an annular reinforcing grid member 16a, a back-up wall 16b, and a top ring 160, which is positioned over the grid member 16a and extended between the screen 16 and the back-up wall 16]), are constructed so as to form a first screen assembly 18 which has a stock receiving chamber 1811 which is in fluid communication with the outlet chamber 17. A second screen assembly 19 is positioned radially inwardly of the screen assembly 18 and substantially concentric therewith, The screen assembly 19 is constructed of a screen 20, a reinforcing grid member 20a, a back-up wall 20b, and a top ring 200. The back-up Wall 2011 also forms part of the supporting structure within the main body 12.

The reinforcing members 16a and 20a serve to support the screens 16 and 20 against the pressure exerted thereon by the incoming material. Material which is delivered to the screening apparatus 10 will fill the chamber 15 and flow over the cylindrical screen assembly 18 to fill a chamber 25 located between thescreen assemblies 18 and 19. Therefore, the material which is carried over into chamber 25, Will pass through the screen and is col lected in the outlet chamber 17, also, the material which is supplied to the chamber 15 will pass through the screen 16 and is collected in the outlet chamber 17. The desired constituent of material which is collected in the receiving chamber 17 is then delivered to a main outlet 27.

Therefore, according to the new and improved screening arrangement of the above invention, the desired constituent of pulp which is delivered to the main outlet 27 is screened by passing the material through screens in a direction radially inwardly of the screening apparatus. This feature eliminates the dewatering effect on the particles being screened, thereby giving a more uniform c011- sistency of the desired constituent of the material.

The heaviest undesired constituent of the material, such as knots, is separated by a plurality of actions but chiefly by centrifugal force and is collected in a receiving chainber 28 whereupon this undesired constituent of the material is delivered to an outlet 29. Still a further undesired constituent of the material, which is heavier than the desired constituent of material, is separated by gravitational means and falls to the bottom of chamber 15. The bottom of chamber 15 forms a trough 30. An outlet 31 communicates with the trough for receiving the undesired material collected thereby. Another trough 33 is located at the bottom of chamber 25 for collecting the constituent of material unacceptable to the process and which is carried over the top of the screen assembly 18. An outlet 34 communicates with the trough 33 for receiving the undesired constituent of material collected thereby.

One or more rotatable foils 35 extend axially of the screen assembly 18 and radially outwardly thereof and immediately adjacent the radially outermost surface thereof as indicated by the dotted lines shown in FIGURE 1. In the preferred embodiment of the present invention the plurality of foils 35 are spaced equally apart around the periphery of the screen assemblies 18. The foils 35 are rotated to clean the surface of the screen member 16 of materials which would otherwise clog the screen: Some of the undesired constituents of the material which are removed from the screen member 16 will fall to the bottom of the chamber 15 into trough 30 and be removed by outlet 31, and some of the undesired material will be carried in suspension over the top of the screen assembly 18 and ultimately collected within the trough 33 and removed by outlet 34.

In a similar fashion a plurality of equally spaced foils 37 extend axially and radially outwardly of the screen assembly 19 and immediately adjacent thereto as seen in FIGURE 1. The foils 37 are also rotated to remove undesired constituents of the material from the surface of the screen member 20 which would otherwise clog the screen. This undesired constituent of material is ultimately collected within the trough 33 and removed via outlet 34.

The housing 12 consists of an upper portion 40 and a lower portion 41 which are fastened together by a plurality of bolts 42 engaging flanges 43 and 44 of the upper and lower portions 40 and 41 respectively. The receiving chamber 17, which communicates with the main outlet 27, is formed by an involute 45 which has the major diameter thereof at the outlet 27, a pair of openings 46 and 47 are provided in one side of the involute 45 in a plane perpendicular to the axis thereof and concentric therewith. The openings 46 and 47 are in direct communication with the space between the screen assemblies 18 and 13.

A support member 48 which also forms the back-up wall 20b of the screen assembly 19, is formed concentrically and integrally within the lower portion 41 and extends upwardly within the upper portion 411. Located concentrically within the support member 48 is a sleeve 49. A shaft 50 is journalled by bearings 51., 52), 53 and 54 which are carried within the sleeve 49. Retainer caps 56 and 57 are secured respectively to the upper and lower ends of the sleeve 49 for retaining the bearings 51, 52, 53, and 54 and the shaft 50 therein. A cover 60 is secured to the upper end of the support member 48, and a seal 61 is carried between the shaft 50 and the cover 60.

A hub 64 is removably connected to the upper end of the shaft 50 and is prevented from rotating relative to the shaft by a key 65. A contoured nut 66 threadably engages theshaft 511 to retain the hub 64 in place. One or more arms 68, indicated by dotted lines in FIGURE 1, extend outwardly from a ring 69 which is secured to the hub 64. Each ofthe arms 68 serves to carry one of the foils 35, as seen in FIGURE 1. Also connected to the ring 69 are one or more arms 70, and each of the arms 70 serve to carry one of the foils 37. It will be understood that each of the foils 35 or 37 may be fixedly connected to their asso ciated arm or may be removably connected thereto.

The foils 35 have bosses 72 which engage a stiffener ring 73 located radially outwardly of the foils. The ring 73 is connected to all of the foils 35 and serves to prevent the foils 35 from flexing axially, which action would cause a gap between the foil 35 and the bottom portion of the screen member 16.

The top portion 40 of the housing 12 is provided with an inlet passage which forms an involute. The involute 80 has an opening on the inside arcuate portion thereof communicating with the interior of the housing 12 for delivering the material to be screened to the chambers 15 and 25.

A cover 82 is secured to the upper portion 40 of the housing 12 by a plurality of studs 83 and nuts 84. A threaded fitting 85 is provided on the cover 82 and may be connected to suitable piping means.

The lower end of the shaft 50 extends into a space within the base 11 and is connected to a multiple V-belt pulley 89. The pulley S9 is rotated by a plurality of belts which are connected to a suitable power source.

Although the specific embodiment of the present invention shows single outlets 29, 31 and 34 for receiving undesired constituents of different character, it is not to be construed in the limiting sense. The housing 12 may have a plurality of outlets for receiving each different undesired constituent of material that is delivered to the outlet 29. That is, the housing 12 may have a plurality of outlets around the housing to receive the undesired constituent of material which is received by the outlet 31. Similarly, the housing 12 may have a plurality of outlets in communication with the chamber 25 for receiving the undesired constituents of material therefrom.

The housing 12 may be provided with water dilution means (not shown) to introduce water into the chamber 15 in a direction substantially tangential to the direction of rotation of the foils 35 and .37. The water dilution means may be provided with a valve for controlling the quantity of water which is to be added to the chamber 15.

According to the present invention, each of the foils 35 is constructed of two members as best seen in FIGURES 2 and 3. The stationary foil member 35a passes in close proximity to the screen member 18 while the pivotable foil member 35b can be in one of two positions. When the pivotable member 35b is in the position shown by the solid line of FIGURE 2, the foil is in the active position and acts as a non-contacting doctor blade to wipe the surface of the screen of knots and large chips etc. On the other hand, when the pivotable member 3512 is in the position shown by the broken line, the pivotable member is said to be in the passive position. In the passive position, the blade is positioned against the top surface. of the stationary portion of the foil 35a to create additional drag during rotation of the foil member. This tends to throw the heavy particles, such as knots, toward the outer wall of the screen housing and into the involute shaped chamber 28. Also, when the screen device of the present invention is used to handle a raw cook, for example, the speed of the foils may be increased and the blade, in the passive position, would pump out the heavier uncooked fiber bundles which would otherwise quickly plug-up the screen 18. Adjustment of the pivotable member 351) in either the active or passive position is accomplished by internal means, indicated by solid and broken line 100 which includes hydraulic actuating means 100a connected to the foil members and therefrom through the center of the rotatable shaft 50. It is noted that in the active positions of the elongated pivotal foil members 35b the distal ends 35d thereof, that is, the ends thereof farthest from the shafts 350 on which the pivotal members are mounted, are disposed radially inwardly of the axes of their respective shafts 35c with respect to the axes of their respective screens 18 and 20. In the passive positions of the pivotal foil member 35b the distal ends 35a are disposed radially outwardly of the shafts 350. By virtue of this arrangement the effectiveness of the pivotal foil members 35b in performing the functions set forth hereinabove is enhanced.

Therefore, the screen apparatus of the present invention is provided with foil means which performs the func tion of actively pulsing the screens 18 and 19 to avoid plugging of the screens as well as providing means for centrifugally removing knots and other large materials. These knots are delivered to an external centrifugal separator 101 and therefrom to a sump settling chamber 102 which has the output thereof connected to a rotary star valve 103. It will be noted that knots are separated from good fiber by introducing in the peripheral portion of chamber 28 a liquid which can be introduced into the chamber by conventional means as indicated by reference numeral 104.

Seen in FIGURE 4 is a more detailed showing of the external centrifugal separator 101, the sump settling chamber 102 and the rotary star valve 103. The external centrifugal separator 101 includes an inlet 106 which is connected to a main body portion 107. The inlet 106 may be connected to either all of the outlets 29, 31 and 34 or may be connected to only the outlet 29, in which case the other outlets 31 and 34 would be connected to additional inlets (not shown). The centrifugal separator 101 has an outlet 108 extending from the top portion thereof which provides means for directing acceptable fiber free from knots which is then fed back to the screening apparatus through the top cover portion 82. The separated material containing knots passes through an outlet 109 into the sump settling chamber 102.

The sump settling chamber includes a conduit 110 which is connected to elutriation liquid. The output of the settling chamber 102 is applied to one of the receiving chambers 111 of the rotary star valve 103. The rotary star valve 103 includes six receiving chambers 111, 112, 113, 114, 115 and 116. The stock delivered to the receiving chamber 111 is conveyed around the rotary star valve 103 and delivered to an outlet conduit 117. At this point, chamber 111 will be in the position as chamber 114 is shown.

The settling chamber 102 includes an emergency exit conduit 118 which has connected thereto a sensing and control device 119 which may sense either the quantity of material within the chamber or the pressure therein to open a valve in the conduit by means of a linkage 120. Therefore, should the removed material enter the settling chamber faster than it is leaving through the rotary star valve, the emergency exit may be operated.

The conduit 110 receiving the elutriation liquid which is free of fiber and which is injected continuously into the chamber is used to maintain a high pressure within the chamber and to make-up for losses. An additional feature of the knotter screen of the present invention is that the acceptable fiber out of the conduit 108 is delivered back to the stock screen 10 for additional processing. This fiber is delivered to the top portion of the stock screen 10 with little difficulty in view of the high rotational velocities of the screening device the top portion of the device remains at a low pressure. Therefore, the amount of equipment necessary for proper handling of the secondary flow can be reduced thereby simplifying the introduction of stock back into the system from the external centrifugal separa- 6 tor. It will be understood that the stock screen 10 will continue its separating function and that other reject openings, such as 31 and 34, will remove shives and slivers of smaller size during the normal screening process and only in emergencies switch the stock so removed to the inlet of the external centrifugal separator 101. Furthermore, dilution means may be incorporated in the stock screen 10 to control the consistency of the pulp at the screen plates.

Therefore, the present invention provides a screening apparatus which removes knots or other large particles from a slurry of wood pulp. It will be understood that variations and modifications may be effected Without departing from the spirit and scope of the novel concepts of this invention.

I claim as my invention: 1. A screening apparatus of the character described for removing knots from wood pulp comprising a housing having a plurality of openings defining a single inlet and a multiplicity of outlets, first and second cylindrical screen members positioned within said housing and concentric with one another, an involute shaped space defined by said housing substantially concentric therewith having an opening on one side thereof facing radially inwardly of said housing,

said involute being in fluid communication with said inlet, first and second foil means concentrically rotatably carried within said housing and disposed respectively adjacent the radially outermost surfaces of said first and second screen members,

each of said foil means including a pivotal member positioned at the leading edge of said foil means, said pivotal member being positionable in an active position to cause wiping of the screen and positionable in a passive position to subject the material adjacent the screen to centrifugal force thereby causing removal of knots, drive means for rotatably driving said first and second foils within said housing and hydraulic actuating means connected to said foil means for hydraulically positioning said pivotal member to said active and passive positions. 2. A screening apparatus of the character described for removing knots from wood pulp comprising a housing having a plurality of openings defining a single inlet and a multiplicity of outlets, first and second cylindrical screen members positioned with said housing and concentric with one another, an involute shaped space defined by said housing substantially concentric therewith having an opening on one side thereof facing radially inwardly of said housing,

said involute being in fluid communication with said inlet, first and second foil means concentrically rotatably carried within said housing and disposed respectively adjacent the radially outermost surfaces of said first and second screen members, and drive means for rotatably driving said first and second foils in a predetermined direction within said housing,

each of said foil means comprising a stationary foil member, a shaft mounted on said stationary foil member at the leading edge thereof and an elongated movable foil member mounted on said shaft and extending from said leading edge, said movable foil member being pivotal between first and second positions at which the distal end thereof is disposed respectively radially inwardly and outwardly of the axis of said shaft, said movable foil member at said first position thereof extending forwardly of said leading edge in said direction of rotation and in said second position thereof extending rearwardly of said leading edge.

3. A screening apparatus of the character described for screening fibrous material to remove knots therefrom comprising a housing having inlet and outlet means spaced apart on said housing,

a screen assembly positioned within said housing substantially coaxial therewith,

foil means positioned adjacent the radially outermost surface of said screen assembly and rotatable with respect thereto,

pivotal means pivotally secured to said foil to be posiuoned in an active pos tion to scrape the screen and in a passive position to impart centrifugal force to undesired material,

a first chamber radially inwardly of said screen assembly for receiving desired stock passing through said screen assembly,

a second chamber radially outwardly of said foil means for receiving undesired stock, and

hydraulic actuating means connected to said foil means for hydraulically positioning said pivotal member to said active and passive positions.

References Cited UNITED STATES PATENTS 3,029,951 4/1962 Cannon 210-298 3,174,622 3/1965 Lamort 209273 3,223,239 12/1965 Dick 209273 X 3,387,708 6/1968 Salomon et al. 209273 3,420,373 1/1969 Hunter 209--'273 FRANK W. LU'ITER, Primary Examiner 

